In design developing and manufacturing of a variety of turbines such as a steam turbine and a gas turbine, it is required to measure vibration occurring at a turbine moving blade for ensuring reliability as preventing an accident as well as improving performance.
A conventional apparatus to measure blade vibration adopts a method to measure blade passing timing by using a proximity sensor and to obtain vibration based on time difference of the passing timing.
With the conventional blade vibration measuring apparatus, it is required to accurately measure the blade passing timing at a high sampling frequency being several hundred MHz or higher. Accordingly, it is required to prepare a data acquisition device which has a high sampling frequency and high time resolution capability.
Further, to obtain high time measurement accuracy, attentiveness is necessary not only for performance of the acquisition device but also for transmission time of a measurement signal. In addition, measured phase difference (time difference) is required to be converted into a displacement. Accordingly, there is a problem that much time and cost are required for measurement preparation and measured data analysis.
On the other hand, there is a method to directly measure blade vibration by using a contactless displacement sensor instead of a proximity sensor.
With this method, since measurement is performed at a sampling frequency on the order of several hundred kHz, time resolution capability required for a data acquisition device is relatively low and preparation of a measurement system and data analysis are relatively easy.
However, when a large-sized rotational blade such as a final-stage blade of a steam turbine or the like is to be measured, displacements at a constant position cannot be captured owing to sampling incapability to catch up blade revolution speed. Accordingly, it is difficult to perform measurement of blade vibration at high accuracy.